Ibis invasion

Australian white ibis - or 'tip turkeys' as many call them - are a nuisance in cities, especially in the spring breeding season. But scientists fear they may become extinct as more pressure is put on their native and adopted environments, writes Abbie Thomas.

Dressed for lunch: the white ibis is a familiar sight in Sydney's parks.
Image: John Martin [more pics]

You're sitting in the park, enjoying a sandwich during lunch when a long, probing beak comes slyly into view and deftly confiscates your pastrami on rye.

You've just been robbed by the Australian white ibis, Threskiornis molucca, and you wouldn't be the first victim.

Ibis are especially bold in spring as they forage for food to feed their hungry chicks. They're an imposing sight, a black and white bird standing almost three-quarters of a metre tall with a bald black head, long purplish legs and distinctive, down-curved beak.

In recent years, white ibis have become a common sight in the cities of east coast Australia, especially Wollongong, Sydney, the Gold Coast, Brisbane and Townsville.

Needing to be near water to breed, these ibis have taken over ponds and creeks in parks and established nesting colonies in palm trees near waterways. Here they can make themselves very unpopular, messing up the water and grass with their faeces, tipping over rubbish bins and cadging food from picnickers.

Recent headlines such as Pests not just in the central ibisness district (Sydney Morning Herald 15/11/07) and Birds of a feather stink together: our ibis scourge (The Glebe, 22/8/07), sum up the general community feeling towards these native birds.

But despite their ubiquity, the days of the ibis may be numbered. Although plentiful now, at least one Sydney researcher fears they may eventually become extinct, a victim both of their own success and of our scientific ignorance.

Population explosion

It's a boy and a girl and a boy... ibis have up to three clutches of three chicks a year
Image: Ursula Munro [more pics]

Ibis are good breeders, producing up to three clutches of three fledglings each season. If they lose a batch of eggs to a predator, they are able to lay more eggs in a week.

Where they do set up shop, numbers can become quite large, says ibis researcher Ursula Munro from the University of Technology Sydney. She estimates that one colony in Sydney's Centennial Park (now largely eradicated) had 1500 birds at the peak of the breeding season.

Richard Major from the Australian Museum and his colleague John Martin from the University of Wollongong do a fortnightly count of ibis in the Sydney region. The most recent puts the Sydney population at around 5000 (about 800 are juveniles), with the Eastern Creek rubbish tip alone hosting up to 800 birds on any day.

Ibis have embraced the inner city lifestyle, in part, because they are highly adaptable. In the wild, their favourite food is native crayfish, mussels and insects. But a radio tracking study by Martin of the birds during their visits to rubbish tips at Belrose, Lucas Heights, Eastern Creek and Gosford, found they will scavenge a wide range of food, although there is scientific uncertainty about how well the birds do on such a diet.

"2002 was a critical year," says Major. "This was when the first big colony set up in [the Sydney suburb of] Bankstown and started to cause anxiety with the local community."

By 2003, up to 1000 ibis were breeding in the Sydney suburb of Bankstown, according to the NSW National Parks and Wildlife Service. It estimated the colony was the largest outside the Macquarie Marshes, their natural breeding wetland in inland NSW.

City councils are under a lot of pressure to do something, so eradication programs have been carried out in several nesting sites. In Centennial Park, a once large population has been greatly reduced by removing nesting vegetation, mainly palms from islands in the ponds. Similarly, a colony at Cabramatta Creek in south western Sydney was significantly reduced using the egg-oil technique.

The birds' eggs are sprayed with canola oil and left for the parents to incubate. The eggs can't develop because the oil cuts off the air supply to the embryo within, but the parents continue trying to incubate the egg for up to two months (eggs normally take about three weeks to hatch). It's a humane technique compared with killing adult birds or chicks, says Major in a research paper on the effectiveness of the method.

Urban drift

However, researchers such as Munro, Major and Martin are very worried about the long-term implications of destroying ibis eggs, chicks and habitat, except from areas where ibis pose a real threat.

It's hard to imagine now, but up until a few decades ago you'd be lucky to see a white ibis anywhere near Brisbane or Sydney.

Their real homes are the massive inland waterways of NSW and Queensland such as the Macquarie Marshes, where they breed in thousands. It is thought a severe drought in the late 1970s drove some ibis towards the coast, seeking water for breeding.

But it's really only been since eastern Australia's most recent drought began that ibis have really started to swamp the suburbs. In 1998 there were 11,000 nests reported from the Macquarie Marshes. But since 2000, there has been no breeding at all recorded in this vast natural habitat, says Major.

Drought and water extraction for agriculture have diminished these once great wetlands, forcing ibis and some other species of waterbirds to seek an alternative place to breed. Cities offer several advantages: permanent water bodies, large open spaces and plenty of food in the form of rubbish bins and of course, landfill sites.

When: White ibis breed from September to April, depending on seasonal conditions. These birds need plenty of available water to trigger breeding.

Where: The Australian white ibis is common and widespread in northern and eastern Australia. It's also found in an isolated region of south-western Australia, but is absent from Tasmania.

A threatened species?

So what's the problem? Surely we can kill a few nuisance birds and still have thousands left?

The problem, says Munro, is that ibis can live for a very long time.

"We don't know exactly how long, but one specimen caught in Victoria was 28 years old. We don't know at what age they stop breeding," she says. "We can go on destroying eggs and nests for years, and not see much of a difference in the adult population. If we take off the recruits [eggs] we don't see an immediate effect of this management."

Adding to this complex picture is the fact that most ibis don't stay in cities all year round. Once they've bred, perhaps two thirds of the population leave and fly north, a few as far as Papua New Guinea. The young don't return to the urban areas until they are at least two to three years old, so it makes it more difficult to figure out how many ibis there are, says Munro.

She points out several species of ibis that were once common in other countries are now either near to extinction or locally extinct, including the sacred ibis from Egypt, the giant ibis from Asia, and the Waldrapp ibis from Europe and North Africa.

Major agrees: "By destroying the nests and eggs of white ibis to manage urban populations, you are reducing the population overall [including those individuals] who could potentially fly back to the Macquarie Marshes to breed."

Sharing our cities

Tip turkey: we might not always like 'em, but we have to learn to live with them, say researchers.
Image: John Martin [more pics]

So could ibis and people ever live together in peace? Munro says a compromise is possible. At Lake Gillawarna in Sydney's south west, the local council allow ibis to breed on islands in the lake. "I like that approach very much," she says.

Major says if birds are breeding near airports, they pose a danger and the nest should be removed.

"But we should remember these are native birds, and they are under stress. We should cut them a bit of slack," he says.

"Seeing them in the cities is a real alarm bell to me of what's happening to those inland wetlands."

Whatever the solution, the problem is not going away. Recently, pelicans and straw-necked ibis have also been seen hanging around Sydney's rubbish tips and suburban fringes. If the wetlands continue to dry up, they could be the next in line to share your Sunday picnic.